1. Technical Field
The present invention relates to an electric rotary shaver in which inner cutters rotate while being caused to be in contact with substantially circular disk form outer cutters, so that hair that advances into the slits in the outer cutters is cut by the inner cutters.
2. Description of the Related Art
Electric rotary shavers that have a plurality of outer cutters are known widely. In one type of such electric shavers, two outer cutters are installed side by side in close proximity; and in another type, three outer cutters are installed at vertices of an imaginary equilateral triangle. In these electric rotary shavers, in order to improve the cutting ability, the respective outer cutters are provided so that they are independently movable in the axial direction and tiltable, so that the outer cutters move in conformity to the curvature of the shaving surface.
Japanese Patent No. 2853812 discloses a shaver in which the shaving units that have inner cutters provided in outer cutters are mounted on a holding plate, and this holding plate is fastened to the inside walls of a cutter frame (holder). The holding plate comprises a plurality of arms that advance and retract from the center toward the outside and vice-versa, and the distal ends of the arm elements are engaged with and disengaged from the inside walls of the cutter frame. The shaving units are mounted on the holding plate laterally from the sides; and in the mounted state, the shaving units are elastically held by elastic arms formed as an integral part of the holding plate so that the shaving units are movable slightly upward and downward.
In the above-described electric shaver which has thus two outer cutters, the holding plate is held on the inside walls of the cutter frame. However, no electric shaver in which the holding plate is held in the cutter frame between two outer cutters is known.
In the electric shaver disclosed in Japanese Utility Model Publication No. H02-14748, the entire outer circumferential edges of the outer cutters are retained by a holding body that holds the inner cutters, and this holding body is pressed against the outer cutters by springs. More specifically, a locking body is detachably mounted on the cutter frame, the locking body is provide with a plurality of anchoring rods that protrude in the radial direction, and the anchoring rods are engaged with and disengaged from the cutter frame; and in addition, the holding body is pressed by a spring that is installed in the locking body.
FIG. 8 shows the internal structure of the cutter frame of a conventional electric shaver (which are not of the above-described prior art), and FIG. 9 shows the cross section of this cutter frame.
In this electric shaver, three round outer cutters 1 are installed in the outer cutter holder 2 so that they are positioned at vertices of an imaginary equilateral triangle, and the respective outer cutters 1 are anchored to the outer cutter holder 2 so that they are movable in the axial direction and tiltable. The reference numeral 3 is an inner cutter holder, and three inner cutters 4 are provided in a freely rotatable manner. In this inner cutter holder 3, two projections 5 are provided so that they protrude in positions separated in the circumferential direction of the outer cutter 1 for each outer cutter 1, thus preventing the projections 5 from interfering with the outer cutter holder 2.
The center of the inner cutter holder 3 is elastically supported on the cutter frame 7 by a locking bolt 6. In other words, a nut 8 is inserted in the center of the cutter frame 7, and the inner cutter holder 3 and a compression coil spring 11 are disposed between a knob 10 and a locking ring 9 anchored to the locking bolt 6. The inner cutter holder 3 is pressed toward the locking ring 9 (i.e., toward the tip end of the locking bolt 6) by the coil spring 11.
In the structure described above, when the tip end of the locking bolt 6 is screwed into the nut 8, the inner cutter holder 3 elastically presses the outer cutters 1 by the coil spring 11. In other words, the circumferential edges of the outer cutters 1 are pressed by the coil spring 11 via the inner cutter holder 3 which forms an integral unit with the projections 5.
When the cutter frame 7 is mounted on the shaver main body (not shown), the inner cutters 4 are connected to the drive shaft (not shown in the figures) of a motor installed inside the shaver main body and rotated. This drive shaft is allowed to advance and retract in the axial direction with a return habit in the direction of protrusion, so that the drive shaft elastically presses the inner cutters 4 against the inside surfaces of the outer cutters 1. Furthermore, three supporting projections 12 (only one is shown in FIG. 9) that support the outer cutter holder 2 in the vicinity of the vertices of an equilateral triangle are formed on this shaver main body in a protruded fashion.
In the electric shaver disclosed in the Japanese Patent No. 2853812, the range of possible movement of the shaving units consisting of the outer cutters and inner cutters (i.e., the range of axial movement and the tilting range) is limited to the range of possible movement of the elastic arms that form integral parts of the holding plate, and thus this range of possible movement is unavoidably extremely small. As a result, the outer cutters cannot sufficiently conform to the indentations and projections and also the inclinations of the shaving surface (skin). Thus, the problem is that the shaver does not have good shaving characteristics.
In the electric shaver shown in the Japanese Utility Model Publication (Kokoku) No. H02-14748, a holding plate that holds the inner cutters is elastically pressed against the outer cutters. Accordingly, upward and downward movement of the outer cutter is accomplished by the longitudinal displacement of this holding plate. However, when the holding plate is removed upon clean of shaving debris, the outer cutters fall out of the cutter frame. Accordingly, in cases where the number of outer cutters is large (e.g., three), attachment and detachment of the outer cutters are bothersome, and handling of the outer cutters is thus difficult.
In addition, in the electric shaver of Japanese Utility Model Publication (Kokoku) No. H02-14748, since the entire outer circumferential edges of the outer cutters are pressed by the holding plate, the holding plate is greatly offset by even a slight displacement of one of the outer cutters, thus affecting the holding of the other outer cutters.
In the conventional example shown in FIGS. 8 and 9, the nut 8 into which the tip end of the locking bolt 6 is screwed is inserted in the cutter frame 7, and this area is surrounded by the outer cutter holder 2. Accordingly, it is necessary to increase the spacing between the outer cutters 1 in the vicinity of this nut 8; and in the case of a shaver that includes three outer cutters, the spacing of the respective outer cutters needs to be sufficiently large, or the diameter of the respective outer cutters needs to be sufficiently large. This, however, causes a problem, which is an increase in the size of the cutter frame. Likewise, in the case of a shaver that involves two outer cutters, the spacing of the outer cutters needs to be large. Thus, the problem in the structure of FIGS. 8 and 9 is serious.